The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers.
Ester group containing polymers are well-known additives for improving the fluidity characteristic of lubricating oils. Polyacrylate, particularly polymethacrylate ester polymers, and esterified carboxy-containing interpolymers are well-known and are widely used for this purpose.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of machinery, in suspension rather than allowing them to deposit on the surfaces of parts contacted by the lubricant.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, "Lubricants and Related Products", Verlag Chemie Gmbh (1984), pp 185-193); C. V. Smalheer and R. K. Smith "Lubricant Additives", Lezius-Hiles Co. (1967); M. W. Ranney, "Lubricant Additives", Noyes Data Corp. (1973)), pp 92-145, M. W. Ranney, "Lubricant Additives, Recent Developments", Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, "Synthetic Oils and Additives for Lubricants", Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
It is desirable that the viscosity improver or dispersant viscosity improver not adversely affect the low-temperature viscosity of the lubricant containing same. Frequently, while many viscosity improvers or dispersant viscosity improvers enhance the high temperature viscosity characteristics of lubricating oil, that is, they reduce the loss of viscosity with increasing temperature, low temperature properties of the treated lubricant become worse.
One of the major requirements for automatic transmission fluids has been improved low temperature performance as demonstrated by a maximum Brookfield viscosity of 20,000 centipoise at -40.degree. C. The viscosity modifier can have a major impact on the low temperature performance. Such characteristics are also desirable in other applications such as in gear lubricants. The copolymers of this invention are also useful in many other lubricating oil compositions including, but not limited to engine oils, hydraulic oils, industrial oils, etc.
Accordingly, it is desirable, and a primary object of this invention, to provide compositions that reduce the extent of loss of viscosity at high temperatures while not adversely increasing the low temperature viscosity of lubricating oil compositions.
A particular object is to provide novel additive concentrates containing multi-purpose lubricant additives.
A more specific object is to provide multi-purpose additives directed to improving the viscosity and dispersant properties of a lubricating composition.
Yet another object is to provide lubricants having improved dispersant and viscosity properties.
Another object is to provide additive concentrates for lubricants, which additive concentrates contain esterified interpolymers that are resistant to shearing.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
Various pour point depressants, additives which reduce the temperature at which oil will flow freely, have been developed and those to reach the commercial market have primarily been organic polymers, although some monomeric substances such as tetra (long chain alkyl) silicates, phenyl tristearyloxy-silane, and pentaerythritol tetrastearate have been shown to be effective. Presently available commercial pour point depressants are believed to be represented by the following types of polymeric materials: polymethacrylates, for example, copolymers of various chain length alkyl methacrylates (see, for example, U.S. Pat. No. 2,655,479); polyacrylamides (see, for example, U.S. Pat. No. 2,387,501); Friedel-Crafts condensation products of chlorinated paraffin wax with naphthalene (see, for example, U.S. Pat. Nos. 1,815,022 and 2,015,748); Friedel-Crafts condensation products of chlorinated paraffin wax with phenol (see, for example, U.S. Pat. No. 2,191,498); and vinyl carboxylate, such as dialkyl fumarate copolymers (see, for example, U.S. Pat. Nos. 2,666,746; 2,721,877 and 2,721,878).
Esters of maleic anhydride/alpha-olefin copolymers have been suggested as pour point depressants. For example, U.S. Pat. No. 2,977,334 describes the use of copolymers of maleic anhydride and ethylene which are esterified with low or high molecular weight alcohols and/or amidized with an amine. These resins are described as being useful as pour point modifiers, gelling agents, thickeners, viscosity improvers, etc., for mineral and synthetic oils including functional fluids and lubricating oils. U.S. Pat. No. 2,992,987 describes a class of lubricant additives useful as pour point depressants which are ethylene-maleic anhydride copolymers esterified to 80% or more, preferably 90-100%, with a mixture of straight-chain saturated hydrocarbon alcohols having from 8 to 24 carbon atoms. The unesterified carboxylic groups can be left unreacted or can be reacted with such materials as ethylene or propylene oxide alcohol esters, or lower-dialkyl-amino-lower-alkylene-amines. U.S. Pat. Nos. 3,329,658 and 3,449,250 describe copolymers of maleic anhydride and alpha-olefins such as ethylene, propylene, isobutylene or vinyl aromatic compounds such as styrene as being useful dispersancy and detergency additives for oils, as well as pour point depressants and viscosity index improvers. The copolymer is esterified to about 30 to about 95% with aliphatic alcohols or mixtures of alcohols having from 10 to 20 carbon atoms, and the remaining carboxyl groups are reacted with an amine of the following formula: ##STR1## where R.sub.1 and R.sub.2 are selected from the group consisting of aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms and the cyclohexyl radical, R.sub.3 is an aliphatic hydrocarbon radical having from 2 to 4 carbon atoms, and R.sub.4 is selected from the class consisting of hydrocarbon atom and aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms.
U.S. Pat. Nos. 3,702,300 and 3,933,761 describe carboxy-containing interpolymers in which some of the carboxy radicals are esterified and the remaining carboxy radicals are neutralized by reaction with a polyamino compound having one primary or secondary amino group and at least one mono-functional amino group, and indicate that such interpolymers are useful as viscosity index improving and anti-sludge agents in lubricating compositions and fuels. The patentee indicates that it is critical that the mixed esters described in these patents include both relatively high molecular weight carboxylic ester groups having at least eight aliphatic carbon atoms in the ester radical and relatively low molecular weight carboxylic ester groups having no more than seven aliphatic carbon atoms in the ester radical.
U.S. Pat. No. 4,604,221 relates to interpolymers similar to those described in the aforementioned '300 and '761 patents, except the ester groups contain at least 8 carbon atoms in the ester radical.
U.S. Pat. No. 5,124,059 describes esters of similar interpolymers characterized by the presence within its polymeric structure of the following groups which are derived from carboxy groups of said interpolymer:
(A) at least one carboxylic ester group having at least 8 aliphatic carbon atoms in the ester group; PA1 (B) at least one carboxylic ester group having an ester group of the formula ##STR2## wherein R is a hydrocarbyl group of about 1 to about 50 carbon atoms, R' is a hydrocarbyl group of about 1 to about 50 carbon atoms, y is a number in the range of zero to about 50 and z is a number in the range of zero to about 50 with the proviso that both y and z cannot be zero; and optionally PA1 (C) at least one carboxylic ester group having no more than 7 aliphatic carbon atoms in the ester group. PA1 said ester being characterized by the presence within its polymeric structure of each of the following groups which are derived from the carboxy groups of said interpolymer: PA1 (D) a carbonyl-amino group derived from an amino compound having an average of from 1 to about 1.1 primary or secondary amino group, wherein the molar ratio of (A):(B):(C):(D) is (20-70):(80-30):(0-20):(0.1-10).
U.S. Pat. No. 3,956,149 issued to Coleman relates to a lubricant or fuel composition containing a nitrogen-containing ester of a carboxy-containing interpolymer.
U.S. Pat. No. 3,959,159 issued to Coleman relates to lubricating compositions containing a nitrogen-containing mixed ester of a carboxy-containing interpolymer.
U.S. Pat. No. 4,284,414 issued to Bryant relates to a crude oil composition containing mixed alkyl esters of a carboxy-containing interpolymer.
U.S. Pat. No. 4,180,637 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing copolymer.
U.S. Pat. No. 4,200,720 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing interpolymer.
U.S. Pat. No. 3,085,994 issued to Muskat relates to a carboxy-containing interpolymer.
U.S. Pat. No. 3,388,106 issued to Muskat relates to a process for making a carboxy-containing interpolymer.
U.S. Pat. No. 3,392,155 issued to Muskat relates to a polyoxy alkylene glycol ester of a carboxy-containing interpolymer.
U.S. Pat. No. 5,157,088 relates to nitrogen-containing esters of carboxy-containing interpolymers having relatively low inherent viscosity.
U.S. Pat. No. 4,088,589 relates to lubricating oils blended from petroleum distillates and, if desired, a bright stock containing waxy or wax-like components and modified by the presence of copolymeric ethylene-higher alpha-olefins viscosity index improving agents, having their low temperature performance improved when said copolymer contains a minor weight proportion of ethylene by the addition of from 0.15 to 1%, based on the total weight of said lubricating oil composition of a combination of pour point depressants comprising: (a) from about 0.05 to about 0.75 wt. % of an oil-soluble condensation product of a chlorinated wax of from 10 to 50 carbon atoms and a mono- or dinuclear aromatic compound; and (b) from 0.05 to 0.75 wt. % of an oil soluble polymer of C.sub.10-18 alkyl acrylate and/or an interpolymer of a vinyl alcohol ester of a C.sub.2 to C.sub.18 alkanoic acid and di-(C.sub.4 -C.sub.18 alkyl) fumarate.
The Society of Automotive Engineers (SAE) has issued a standard, J-300 (December 1995), which defines limits for classification of engine lubricating oils in rheological terms. This standard contains limits for various engine oil viscosity grades. Also included in the standard are discussions of low temperature and of high temperature test methods.
A review of developments in low temperature performance is presented by Schaub, "A History of ASTM Accomplishments in Low Temperature Engine Oil Rheology" in "Low Temperature Lubricant Rheology Measurement and Relevance to Engine Operation", R. B. Rhodes, ed., ASTM, Philadelphia, Pa. (1992), pp 1-19.